Allergy is a disorder of the immune system and is characterized by the occurrence of allergic reactions to normally harmless environmental substances. Allergies are caused by allergens, which may be present in a wide variety of sources, including but not limited to pollens or other plant components, dust, molds or fungi, foods, additives, latex, transfusion reactions, animal or bird danders, insect venoms, radiocontrast medium, medications or chemicals. Common allergic reactions include eczema, hives, hay fever, asthma, and reactions to venoms. Mild allergies like hay fever are highly prevalent in the human population and cause symptoms such as allergic conjunctivitis, itchiness, and runny nose. In some people, severe allergies to environmental or dietary allergens or to medication may result in life-threatening anaphylactic reactions and potentially death, if left untreated. Allergic reactions can occur in three distinct patterns: a) an early phase reaction or acute response, b) late phase reactions and c) potentially chronic allergic inflammation. The early phase of the allergic reaction typically occurs within minutes, or even seconds, following a first allergen exposure, where this early phase is also commonly referred to as the immediate allergic reaction. In the early stages of allergy, a hypersensitivity reaction against an allergen, encountered for the first time, causes a response in Th2 cells, which are a subset of T cells that produce the cytokine interleukin-4 (IL-4). The Th2 cells interact with B cells (lymphocytes that produce antibodies against antigens) and, coupled with the effects of IL-4, stimulate the B cells to begin production and secretion of Immunoglobulin E (IgE).
IgE plays an important role in allergies and allergic reactions. Upon introduction of an allergen, B cells of the respective subject produce large amounts of IgE. The IgE elicits an immune response by binding onto receptors found on basophils and mast cells. When activated, these cells release chemical mediators such as histamine and cytokines that cause the characteristic symptoms of allergy.
A food allergy is an adverse immune response to a food allergen, e.g., a food protein. Common food allergens are found in shellfish, peanuts, tree nuts, fish, milk, eggs, soy and fresh fruits such as strawberries, mango, banana, and apple. Immunoglobulin E (IgE)-mediated food allergies are classified as type-I immediate hypersensitivity reactions. These allergic reactions have an acute onset (from seconds to one hour) and the accompanying symptoms may include angioedema (soft tissue swelling of the eyelids, face, lips, tongue, larynx and trachea); hives; itching of the mouth, throat, eyes, or skin; gastrointestinal symptoms such as nausea, vomiting, diarrhea, stomach cramps, or abdominal pain; rhinorrhea or nasal congestion; wheezing, shortness of breath, or difficulty swallowing; and even anaphylaxis, a severe, whole-body allergic reaction that can result in death. Gupta, et al. (PEDIATRICS Vol. 128 No. 1 Jul. 1, 2011 pp. e9-e17) demonstrated that 1 out of 12 children under the age of 21 years of age have a doctor's diagnosis of food allergies. This epidemic has been reported to be doubling every 10 years for certain nuts (CDC 2009). Moreover, there are still deaths that occur every year due fatal food allergies. Importantly, over $24 billion is spent per year on health care/care costs for food allergic reactions (Gupta, et al. JAMA PEDIATRICS November 2013, Vol. 167, No. 11). This cost is largely due to about 90,000 visits to the ER per year in the U.S. due to food induced anaphylactic symptoms.